Method of treating pulp mill waste cooking liquors



METHOD OF TREATING PULP MILL WASTE COOKING LIQUORS Filed March 10, 19321 INVIEVNTIOR esonaauxommson AI TURKEY Patented Feb. 16. 1937 METHOD OFTREATING PULP WASTE COOKING LIQUORS George H. Tomlinson, Montreal,Quebec, Canada Application March 10, 1932, Serial No. 597,996

11 Claims.

This invention relates to the recovery of chemicals contained in wasteliquors resulting from processes of pulping cellulosic materials. Moreparticularly, it comprises a method and apparatus which has provenespecially useful in connection with the recovery of chemicals'used inthe kraft or sulphate pulping processes.

Various workers in this field have developed recovery processes based onthe idea of introducing waste liquors, in atomized condition, into a hotcombustion or recovery chamber wherein the spray particles, afterevaporation of the water content, are burned in suspension in accordancewith principles similar to those employed in the burning of oils-.orpowdered fuels. In the commercial application of these processesdifficulties so as to consistently produce satisfactory results.

The maintenance of self-sustaining combustiom' satisfactory reducingconditions; and prevention of excessive loss of chemicals through thedraft stack of the recovery chamber presupposes a perfect co-relation ofvarious controlling factors such as the initial concentration of theatomized liquor; the size of the spray particles; and the size, shapeand dimensions of the recovery chamber which is impossible to attain inactual practice, If the liquor is not sufficiently concentrated or ifthe spray particles are too large the number of wet particles reachingthe hearth will be sufficient to prevent further burning or combustion.If the spray is too fine it produces a large number of small particleswhich are carried out of the recovery chamber by the draft. Moreover,-the burning of the particles in the form of a spray necessarily producesa large number of exceedingly fine residual particles containing thechemicals sought to be recovered. These residual particles are alsocarried away, to a greater or lesser extent, by the furnace draft andcreates a condition which necessitates the use of more or lesscomplicated recovery equipment outside the primary recovery chamber inorder to prevent excessive chemical losses. Even with the most carefulregulation of the spray, the burning of the particles in suspension ischaracterized by excessive loss of chemicals through the stack outletand it also produces unsatisfactory reducing conditions since the amountand characterof the carbon produced by the spray combustion does notprovide for eflicient reduction of the sulphates to sulphides.

The present invention has been developed to overcome these diflicultiesand is based on em tirely different principles of operation, Accordingto this invention the liquor is spray-dried in the upper region of avertical stack furnace where it is introduced inthe form of a coarsespray directed against one of the furnace walls. The direction of thespray and the regulation of the size of the particles so thatsubstantially all of the water is evaporated before the particles reachthe wall toward which they are projected is a comparatively simplematter. On reaching. the wall the substantially dry particles adhere andbuild up into a plastic spongy cake which, after some further drying,gradually leaves the wall in the form of lumps which drop tothe bottomof the furnace or recovery chamber where combustion proceeds with greatrapiditysince the .lumps reach the hearth in a porous, spongy statecontaining all or a very. considerable amount of the organic material ina substantially unburned condition. By confining combustion of the or-'ganic material to the lower region or hearth of the recovery chamber;the entire heat value of the fuel constituents of the waste liquor isrendered available foreffecting evaporation of the spray particlesentering the chamber above the combustion zone. To accomplish this itis, of course, 25 desirable that the recovery chamber be designed sothat all of the heat resulting from'combustion on the hearth is causedto ascend through the spraying or drying zone. The surplus heat Iavailable after evaporation of the incoming spray is very considerableand is utilized for the generation of steam in a boiler located at theupper end of the recovery chamber. Owing to .the direct absorption ofheat by the incoming spray particles and by the 'boiler the.developmentof excessive temperatures in' the upper part .of therecovery chamber is prevented so that wallreplacement and othermaintenance dimculties frequently due to excessive temperatures in thispart of the recovery chamber are substantially avoided. Furtheravoidence of these maintenance difiiculties may also be achieved byproviding a relatively thin externally cooled section of wall structureforthe upper part of the recovery chamber in order to prevent bucklingeffect due "to the impingement of relatively cool spray particles on atoo highly heated wall=surface. When the recovery is carried out inaccordance with the principles described herein it is a simple matter'toregulate the spray to pro- 0 duce particles of such large size that thedanger of these particles being carried away in flight is avoided. It isalso possible with this process to effect the self-sustained evaporationand burning of comparatively dilute liquors within the furnace with suchof decomposition and reversion recovery chamber. I have found, forexample, that it is possible, through suitable spray regulation, tosuccessfully dry the liquor when containing as much as two or more partsof water to one of solids but, in practice, it is usually moreeconomical to concentrate the liquor in multiple effect evaporators to amuch higher density, rather than to effect the evaporation of thisexcess water in the furnace. Thus, if the liquor is evaporated to adensity corresponding to one part of water to one of solids, a veryconsiderable surplus of heat becomes available, after evaporation of theincoming spray, for the generation of steam in the boiler.

In recovering the chemicals used in the kraft or sulphate pulpingprocess air is admitted to the recovery chamber onlyat or slightly abovethe hearth, which is formed to slope towards a suitable outlet at thefront of the furnace. This control of the air admission, together withthe free burning characteristics of the combustible material deliveredto the hearth, produces a reducing atmosphere at a point where themaximum'quantity of, reducing material, in an activated form, isavailable for accomplishing the reaction necessary to reduction of thesulphates to sulphides. Due tothe rapid combustion on the hearth thechemicals melt and leave the rapidity as to avoid danger of thesulphides to sulphates. I

Since the amount of dust particles leaving the upper portion of therecovery chamber in an un: altered condition is so small as to bepractically negligible, it will be manifest that the boiler can beoperated efiiciently at high ratings and that the heat in the wastegases can be utilized in an economizer under conditions which are notpossible where the dust losses are substantial as in cases where theliquor is dried and burned in the form of relatively small sprayparticles as heretofore proposed.

In the further description of this invention reference will be had-tothe accompanying drawing wherein I have shown a vertical shaft type ofrecovery furnace in which the process has been successfully carried out.

The recovery chamber or furnace is generally indicated at H. The lowerportion is provided with a soapstone lining l2 and forms a smeltingchamber l3. The bottom M, of the smelting chamber slopes toward anoutlet l5 leading to a the boiler drum discharge spout l6 through whichthe smelt, comprising the recovered chemicals, is delivered to asuitable tank (not shown). The upper portion I! of the furnace above thesmelting chamber I3, is also provided with a suitable refractory lining18. The top of the furnace orrecoverychamber is formed principally by aboiler setting of the water tube'type. As herein shown this settingcomprises the front and rear'headers i9 and 20, connecting water tubes22, and 23. The latter is provided with connections 24 to the headers l9and 20 and is supported at the upper rear corner of the furnace. Therear wall structure of the furnace comprises relatively offset verticalwall portions 25 and 26 and a connecting horizontal wall portion 21. Thevertical wall- 25 extends upwardly beyond the horizontal wall 21 to forma baille 28 spaced inwardly from the lower portion of the vertical wall26. Inclining upwardly and forwardly from the baffle 28 is asecondbaille 29 through which the boiler tubes 22 pass as I shown. In theoperation of the furnace the prodthe boiler.

v and beneath the top furnace wall 3| to the discharge fiue 32 and outthrough the pipe 33.

The liquor to be treated is introduced into the.

upper furnace portion I! through a spray nozzle 34 mounted in a suitableopening in the front furnace wall-30. The liquor is discharged from thenozzle in the form of a coarse spray which is projected against one ofthe side walls 35. When dealing with a coarse spray of this character itis a simple matter to regulate the size of the spray particles so thatall of the particles will reach the wall 35 and will be deprived of thegreater portion of their water content during transit. The size andvelocity of the spray particles discharged will mainly depend upon therequired length of furnace travel to reach the arresting wall surface,which distancewillvary with the furnace size and cross-sectionemployed.The spray particles coalesce on the wall 35 to form a spongy mass asindicated at A. This mass, after some further drying, gradually breaksaway from the wall in the form of porous spongy lumps indicated at 36.All or a very substantial portion of theorganic material originallypresent in the liquor is contained in these lumps and is carried to thehearth in a dry and substantially unburned condition. The combustion ofthe organic material on reaching the hearth is practically instantaneousand is characterized by the rapid production or evolution of activatedcarbon or reactive carbon compounds which, through their exceedinglyhigh aflinity for oxygen, cause the reducing reaction to proceedraphearth formed by'the bottom wall I4 is caused .to pass through theevaporating zone on its way to the outlet pipe 33' and the intensity ofthe heat generated on the hearth is such that the surplus heat availablefor generation of steam in the boiler, after evaporation of the incomingliquor, is very considerable. It may be stated,

' however, that the temperature in the upper part of the furnace orrecovery chamber is relatively low compared with the temperature in thelower portion due to the amount of heat which is directly absorbed bythe incoming spray and by This lowering of the temperature in the upperpart of the furnaceis of advantage in that the refractory lining neednot be replaced asoften as in the case of prevailing types of recoveryfurnaces in which excessively high temperatures prevail in the upperregion of the recovery chamber. portion I! of the furnace becomes toohighly heated the spraying of the relatively cool liquid particlesthereon is apt to cause a certain amount of buckling. In order toprevent this the present invention contemplates external cooling of theIf the lining in the upper furnace portion I! by any suitable, method ofcirculating water or any other fluid in contact therewith. 1 i

Only one nozzle 34 is shown in the present drawing but it will beunderstood that the number and arrangement of nozzles employed inpractice may be varied within wide limits. Usually two nozzles arearranged at a suitable inclination to spray the liquor against both ofthe side walls 35. The number and arrange-' ment of the nozzles may alsobe such as to direct sprays of liquor against the front and rear wallsas well as against the side walls. The invention therefore contemplatesany arrangement of the nozzles which will cause substantially all of thespray particles to reach the wall surface towards which they aredirected in a relatively dry condition and in such manner that thegreater portion of the organic material is subseqently delivered to thehearth in the form of free burning lumps containing the chemicals to berecovered,

together with an abundance of reducing carbonaceous material in anactivated form.

When using a furnace of the type shown in the drawing and operating asdescribed herein it has also been found that the quantity of salt cakeintroduced into the furnace with the waste liquor may be substantiallyincreased as compared with present practice, in view of the fact thatthe amount of reducing carbonaceous material which is present in thereducing zone in an activated condition is considerably in excess ofthat required merely for recovering the chemical content of the wasteliquor. Satisfactory combustion and reducing conditions are maintainedin the lower region of the recovery chamber by supplying air in suitablequantities through the air inlets 31 and 38, the latter being relativelyclose to the hearth l4 and the latter being inclined so that the airadmitted therethrough is directed downwardly towards the hearth. The gasvelocity through the furnace and boiler is regulated in accordancewiththe furnace operating load to maintain effective 1 combustionconditions in the furnace, while avoiding excessive carry-over of theliquor particles into the boiler.

By way of example, and not of limitation, I have successfully carriedout my. process in a refractory-walled vertical stack furnace, as

shown in the drawing, fourteen feet in length by eight feet in widthwith a furnace height at the middle of the side walls 35 of twenty feetbelow a 265 H. P. horizontal tube bank steam boiler.

Kraft black liquor having an average analysis 4 having a dischargeorifice three-eighths of an inch in diameter at a pressure of 40 lbs.per sq. in. and a temperature of 210 F. The nozzles were centrallylocated in the front wall 30 at a level corresponding to a centralfurnace height of about fifteen feet and relatively arranged to directconical sprays of liquor toward opposite side walls 35. Each spraycovered a side wall area of approximately sixty sq. ft. with a length offurnace travel of the liquor particles traveling axially of the nozzleof approximately nine ft. The average size of the spray particlesdischarged was estimated to be not greater than one-tenth of an inch indiameter. With a furnace temperature in the lower section of the furnaceranging from 1900 F.2l00 F. and above the spray level of from 1700F.-1850 'F. the material on the walls had an average analysis of about5% water and dry solids. With a furnace capacity corresponding to 50tons of airdried pulp per day, the gas velocity through the furnace wascomputed to be approximately 365 ft. per minute. Under these conditionsself-sustaining combustion was easily maintained on thehearth, a highpercentage of chemical recovery and reduction obtained, and a high rateof steam generated per ton of liquor fired.

Having thus described my invention, what I claim is:

1. A self-sustaining process of recovering chemicals and heat in astationary recovery furnace of the vertical shaft type from liquorcontaining chemicals and combustible organicv matter which comprisesintroducing the liquor into the upper section of the furnace in a spraysufficiently coarse to cause a major portion thereof to pass'throughhigh temperature heating gases and while in a. resultant stickycondition to collect and coalesce in an adhering mass on an arrestingsurface in heat absorbing relation with e the heating gases, whereby theliquor so treated will be substantially completely dehydrated in theupper section without substantial change in its initial organic contentand lumps of dehydrated material will break away from said mass and fallinto the lower section of the furnace, burning the lumps of dehydratedmaterial falling from said mass in the lower section of the furnacewhereby the included chemicals are smelted,

passing the high temperature heating gases generated in the lowersection upwardly through the spray sufficiently coarse to cause a majorportion thereof to pass through high temperature heating gases'in thedrying zone and while in a resultant sticky condition to collect andcoalesce in an adhering mass on an arresting surface contacted bythe'heating gases, whereby the liquor 'so treated is substantiallycompletely'dehydrated' without substantial change in its initial organiccontent and lumps of dehydrated material break away from said mass andfall into the combustion and smelting zone, burning the lumps-ofdehydrated material falling from said mass in the combustion andsmelting zone without the addition of other combustible matter wherebythe included chemicals are smelted in the combustion and smelting zone,passing the 'high temperature heating gases generated in the combustionand smelting. zone upwardly through the drying zone for the dehydrationof liquor being introduced into the drying zone, and Withdraw-, ing theincombustible inorganic residue in a molten condition from thecombustion and smelting zone. i

3. A self-sustaining process of recovering chemicals and heat in astationary recovery furna e of the vertical shaft type from paper pulp'rz'sidual liquor containing chemicals and comnor in a spraysufiiciently coarse to cause a ma- 4 jor portion thereof to pass throughan ascending stream of high temperature heating gases in the drying zoneand while in a resultant sticky condition to collect and coalesce in anadhering mass on a vertically disposed arresting surface in the dryingzone in heat absorbing relation with the heating gases, whereby theliquorso treated will be substantially completelly dehydrated in thedrying zone without substantial change in its initial organic contentand dehydrated material will separate from said mass and collect in thecombustion zone, burning the lumps of dehydrated material separatingfrom said mass in the combustion zone, and passing the high temperatureheating gases generated in the combustion zone upwardly through thedrying zone for the. dehydration of residual liquor being introducedinto the drying zone.

4. A self-sustaining process of recovering chemicals and heat in astationary recovery furnace of the vertical shaft type from paper pulpresidual liquor containing chemicals and combustible organic matterwhich comprises maintaining an upper drying zone and a lower combustionand smelting zone in the furnace, introducing thelquor in a spraysufiiciently coarse to cause a major portion thereof to pass through anascending stream of high temperature heating gases in the drying zoneand while in a resultant sticky condition to collect and coalesce in anadhering mass on a vertically disposed arresting surface in the dryingzone contacted by the heating gases, whereby the liquor so treated issubstantially completely dehydrated without substantial change in itsinitial organic content and lumps of dehydrated material break away fromsaid mass and fall into the combustion and smelting zone, burning thelumps of dehydrated material falling from said mass in the combustionand smelting zone whereby the included chemicals'are smelted in thecombustion and smelting zone, passing the high temperature heating gasesgenerated in the combustion and smelting zone upwardly through thedrying zone for the dehy-' dration of residual liquor being introducedinto 1567 drymgflone gpd withdrawing the incomterial falling from saidchemicals and bustible inorganic residueina molten condition from thecombustion and smeltingzone.

5. K' s'elfesustaining process of recovering eat in a stationaryrecovery furnace of the vertica haft type from paper pulp residualliquor contain chemicals and com: bustible organic matter mprisesmaintaining an upper drying zone and a ower combustion and smelting zonein the furnace, ducing the liquor through one of the vertical furnacewalls in a spray sufliciently coarseand at sufiicient velocity to causea major portion thereof to pass substantially horizontally across thefurnace through an ascending stream of high temperature heating'gases inthe drying zone and wh le in a resultant sticky condition to collect andcoalesce in an adhering mass on another vertical furnace wall in thedrying zone in heat absorbing relation with the heating gases, wherebythe liquor so'treated will be substantially completely dehydrated in thedrying zone without substantial change in its initial organic contentand lumps of dehydrated material in a porous spongy condition will breakaway from said mass and fall into the combustion and smelting zone,burning .the lumps of dehydrated mamass in the combustion and smeltingzone whereby the included chemicals are smelted inthe combustion andsmelting zone, passing the high temperature heating gases generated inthe combustion and smelting zoneupwardly through the drying zone for thedehydration of residual liquor being introduced into the drying zone,withdrawing the incombustible inorganic residue in a molten conditionfrom the combustion and smelting zone, and withdrawing the heating gasesfrom the furnace above the spray level.

'6. A self-sustaining process of recovering chemicals and heat in astationary recovery furnace of the vertical shaft type from sulphatepaper pulp residual liquor containing chemicals and combustible organicmatterwhich comprises introducing the liquor ina spray directed acrossthe upper section of the furnace and having spray particles of a sizeand velocity sufficient to cause a major portion of the spray particlesto impact .on a vertically disposed arresting surface in the uppersection of the furnace after passing through and being heated by anascending stream of high temperature heating gases sufiiciently to putthe spray particles when impacting in a sticky condition, whereby theimpacting material will adhere to the arresting surface while exposed tothe ascending high temperature gases until the material is in asubstantially dehydrated condition but without substantial change in itsinitial organic content, collecting and burning dehydrated materialseparating from said surface in the lower section of the furnace underchemical reducing conditions whereby the heat generated in the lowersection eifects the liquefaction and reduction therein of the includedchemicals, passing the high temperature heating gases generated in thelower section into the upper section for dehydrating liquor beingintroduced into the upper section, withdrawing the high temperaturegases from the upper section above the spray level, and withdrawing theliquefied chemicals from the lower section.

7. Apparatus for recovering chemicals and heat from liquor containingchemicals and combustible organic matter comprising vertical front, sideand rear walls defining a stationary furnace of the vertical shaft typeof substantially rectangular horizontal cross-section having an uppersection receiving high ing gases from a communicating lower section,spray means in said front wall for introducing the liquor so arrangedthat the liquor is directed in a spray substantially horizontally acrosssaid upper section in intimate contactwith said heating gases and inparticles of such size and at such velocity that they impact against atleast 011%: said vertical'side walls over an extended area n conditionto coalesce thereon in an adhering mas earth at section arranged t0re@ive the substantially dry material falling from said adhering mass,means for supplying air for the confiusticm f the material collecting onsaid hearth in a position temperature heat- 9 the bottom of said lower"of, spray means for introducing the liquor so arranged that the liquoris directed it: a spray substantially horizontally across said uppersection below said heating gas outlet in intimate contact with saidheating gases and in particles of such size and at such velocity thatthey impact against one of said vertical walls in condition to coalesceI thereon in an adhering mass, a hearth at the'bottom of said lowersection arranged to receive substantially dry material from 'sadadhering mass, means for supplying air for the combustion of thematerial collecting on said hearth in a position to radiate heat to saidupper section, a steam boiler above said furnace and having ahorizontally inclined tube bank extending longitudinally of and acrosssaid heating gas outlet,

and an outlet in said lower section for the molten incombustibleresidue.

9. A self-sustaining process of treating paper pulp residual liquor in astationary recovery fur- 1 naceof the vertical shaft type whichcomprises introducing the liquor into the upper section of the furnacein a spray sufficiently coarse and at such velocity as to cause a majorportion thereof to pass through high temperature heating gases andwhilein a resultant sticky condition to collect' and coalesce in an adheringmass on an arresting surface in heat absorbing relation with the heatinggases, whereby the liquorso treated will be substantially completelydehydrated in the upper section without substantial changein its initialorganic content and lumps of dehydrated material will break away fromsaid mass and fall into thelower section of the furnace, buming thelumps of dehydrated material falling from said mass in the lower sectionof the furnace, and passing the high temperature heating gases generatedin the lower section upwardly through the upper section for thedehydration of liquor. being introduced into the upper section.

10: A process of treating paper pulp residual liquorwhich comprisesintroducing the liquor into a vertical furnace in a spray directedacross the upper section of the furnace and formed of that a majorportion of the spray particles im 1 upper section of the furnace afterpassing spray particles of a size and at a velocity such pact on avertically disposed wall surface in the through and being heated by anascending stream of high temperature gases sumciently to put the sprayparticles when impacting in a sticky condition and to cause the sprayparticles to deposit on the wall surface over an extended area in anadhering mass and from which mass dehysection of the furnace for thecombustiontherein of the combustible portion of the separated material,and withdrawing the high temperature gases generated inthe lowersectionof thefurance from the upper section of the furnace after contactingwith liquor being sprayed across the upper section of the furnace.

11. In the operation of a chemical recovery furnace having a furnacechamber of substantial height with a heating gas outletvconfin'ed to theupper section thereof, a hearth at the bottom of the lower sectionthereof and at a substantial distance below said heating gas outlet, anda smelt outlet from said hearth, the process of recovering chemicals andheat from sulphate paper pulp residual liquor which comprises intro-"ducing the liquor into the furnace chamber in a spray directed into theupper section of the furnace chamber and formed ofspray particles of aof separated material on the hearth in a dry porous condition and withsubstantially their initial organic content, supplying air to the lowersection for burning the combustible portion of the separated material onthe hearth under chemical reducing conditions whereby the heat generatedeffects the liquefaction and reduction therein of the includedchemicals, withdrawing the high temperature gases generated through theheating gas outlet after contacting with residual liquor being spra'y'edinto the upper sectio'n,and withdrawing the liquefied chemicals from thelower section through the smelt outlet.

a GEORGE ETCMJNSON.

